1. Field of the Invention
This invention relates to electronic systems, and more particularly to the transmission of electromagnetic signals.
2. Description of the Related Art
An electromagnetic wave propagating through space has orthogonal electric (E) and magnetic (H) field components commonly described in Cartesian coordinates. The concept of using an electromagnetic beam for transmitting information is attractive at high frequencies, such as the frequency band of approximately 20-40 GHz. Transmission of the electromagnetic beam to a destination typically involves the use of a signal-guiding element and one or more amplifiers in a power amplifier module. Functions such as switching and bi-directional amplification are used to accomplish the system.
In U.S. Pat. No. 6,756,866, J. Higgins describes a signal-guiding element in the form of a waveguide that has high impedance structures on its walls to provide phase shifting while maintaining power density across its width for amplification. The surface impedance of the walls is voltage controlled using voltage dependent capacitance which determines the resonant frequency of the wall impedance structure and results in a change of the wave propagation constant and, subsequently, the phase of transmission coefficients (S21 and S12). J. Higgins suggests the use of the impedance structure on all four walls of the waveguide to support simultaneous and active phase control of two linearly and orthogonally polarized microwave or millimeter wave signals. An array amplifier is an array of small amplifiers each with an input antenna and an orthogonally oriented (with respect to the input antenna) output antenna. The amplified wave is polarized orthogonally with respect to the input wave. The combination of such a waveguide and an array amplifier can establish a directional power amplifier module for guiding and amplifying the input signal.
One problem associated with the prior art power modules described above is the unidirectionality of their associated amplifier arrays. Amplifier arrays use input and output antennas that are perpendicular to one another and, because antennas radiate in both upstream and downstream directions, require polarizers to set the direction of gainful propagation. The orientation of the antennas in comparison to the polarization of the return signal prevents bidirectional signal gain for rotationally fixed power modules. If bidirectional signal gain is required, a second power module is typically used. This results in duplicative power modules.